The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:
3GPP third generation partnership project
CA carrier aggregation
CC component carrier
CCE control channel element
DCI downlink control information
DL downlink
eNodeB node B/base station in an E-UTRAN system
DL downlink
E-UTRAN evolved UTRAN (LTE)
HARQ hybrid automatic repeat request
LTE long term evolution (of UTRAN)
LTE-A long term evolution-advanced
PCell primary component carrier/primary cell
PDCCH physical downlink control channel
PDSCH physical downlink shared channel
PUSCH physical uplink shared channel
SCell secondary component carrier/secondary cell
SPS semi-persistent scheduling
TDD time division duplex
UE user equipment
UL uplink
UTRAN universal terrestrial radio access network
The concept of carrier aggregation CA is well established in the wireless communication arts and has been undergoing development for the LTE/LTE-A systems. In CA the whole system bandwidth is carved into multiple component carriers CCs. Specific for LTE/LTE-A, each UE is to be assigned one PCell which remains active and one or more SCells which may or may not be active at any given time, depending on data volume for the UE and traffic conditions in the serving cell. At least one CC in the system is to be backward compatible with UE's which are not capable of CA operation, and the SCells may be similar to the PCell (e.g., with their own set of control channels) or what is termed extension CCs which can be utilized only in conjunction with a full CC (e.g., only traffic channels on the extension CCs). For example, the network can send a resource allocation (a PDCCH) to a UE on its PCell which allocates resources for sending/receiving data on any activated SCell, even an extension carrier. This is known as cross-scheduling (the resource allocation or schedule is communicated on a different CC than the scheduled radio resource is located), and is not limited to only the PCell and extension CCs. The LTE-A system proposes to expand this concept so that it is possible to have one or more SCells in unlicensed radio spectrum (e.g., the ISM band or TV whitespaces).
FIG. 1A illustrates the general CA concept for LTE/LTE-A. For a given UE there is assigned a PCell 100 which by example is backward-compatible with LTE Release 8/9 UEs (and therefore 20 MHz in bandwidth though the various CCs may be defined by different bandwidths). That same UE may also have in its assigned set SCell #1, SCell #2 and SCell #3, which for completeness SCell #3 is shown as being non-contiguous in frequency with the other CCs. Any number of the SCells or none of them may be active for that UE at any given time, as coordinated with the eNodeB. Every UE is to have its assigned PCell always active, and so legacy UEs which are not CA-capable will be assigned one backward-compatible CC and no others.
Each CC will be operating at any given moment with a specific UL/DL configuration, each configuration defining a specific order of DL and UL subframes. The eNodeB may send and the UE may receive DL control information (PDCCH, PHICH) or data (PDSCH) in a DL subframe. Correspondingly the UE may send and the eNodeB may receive UL control information (HARQ) or data (PUSCH) in a UL subframe. The UE gets is schedule of allocated DL and UL resources in a PDCCH which tells which DL and/or UL subframes are allocated for the UE's data. Each specific UL/DL configuration has a channel mapping associated with it, and relevant to these teachings there is a mapping of the UE's UL subframe in which the UE sends data in a PUSCH to a DL subframe in which the UE listens for a PHICH to confirm whether or not the eNodeB properly received and decoded its UL data.
It is expected for 3GPP Release 11 (LTE-A) that there will be the capability for cross scheduling across CCs, and also that the different CCs may have different UL/DL configurations. The latter is to support layer deployment where different CCs provide different coverage and accommodate different traffic, and also inter-band CA and co-existence with other systems in certain frequency bands.
Co-owned international patent application PCT/CN2011/072774 (filed 14 Apr. 2011) details problems that arise when there are different UL/DL configurations on two CCs that are active for a given UE. Namely, for the case that HARQ feedback is sent always on the PCell but maps from the CC on which the resource being acknowledged lies, there is the potential that the UE cannot send its HARQ feedback because the mapped subframe may be for downlink only. That co-owned application discusses a similar problem when cross-scheduling across two CCs with different UL/DL configurations.
These issues arise when there is one or more overlapped subframes in the different CCs as shown by example at FIG. 1B which assumes that there are two CCs configured for a given UE in a TDD system. CC #1 is configured in the TDD UL/DL subframe configuration #0 and CC #2 is configured in the TDD UL/DL subframe configuration #2. Subframe #3 is termed an overlapped subframe because that same subframe in one CC is UL and in the other CC it is DL.
The inventors have also found that for the case of overlapped subframes the UE's blind detection capability is not sufficiently utilized. This relates to the UE's search space, and both the problem and its solution are further detailed in the detailed description section below. To the inventors' knowledge there has been no prior solution to better utilize a UE's blind detection capability for a system with CC-specific TDD UL/DL configurations.
There are references which relate generally to search spaces and blind decoding. Specifically document R1-102741 by Qualcomm entitled SEARCH SPACE AND BLIND DECODES FOR CA (3GPP TSG RAN WG1 #61; 10-14 May 2010; Montreal, Canada) proposes that when some of the configured CCs would be deactivated, more than one search space can be used for scheduling a PDSCH/PUSCH on a CC that is not deactivated. However this document does not appear to suggest how a UE's blind detection capability can be fully exploited when monitoring more than one search space on the activated CCs would exceed a UE's blind detection capability. This is possible for system with CC-specific TDD UL/DL configurations since even if there would be no DL grant for a CC in UL subframe, but there might be UL grant still, which means only part of the blind detection number can be “spare” for a CC in UL subframe. The same issue may exist when the two CCs would be configured with different TDD special subframe patterns. Furthermore, the suggested solution in document R1-102741 is based on the activation/deactivation status of the CCs, which may have issues such as MAC signaling reliability.
Another reference which concerns blind detection in CA is document R1-103084 by Huawei entitled PDCCH BLIND DECODING IN LTE-A (3GPP TSG RAN WG1 #61; 10-14 May 2010; Montreal, Canada). This document proposes that the eNodeB semi-statically configure the maximum number of blind detections for a UE. However, the document itself does not make clear how to use such a higher layer based configuration for systems with CC specific TDD UL-DL configurations, nor does it address the concept of overlapped subframes as noted above. Furthermore, the definition of search space in document R1-103084 does not appear able to scale with the configured number of blind detections, which means it would be difficult to adapt those teachings to at least the current PDCCH search space structure in the LTE/LTE-A systems.
Exemplary embodiments of the invention detailed below more efficiently utilize the blind detection capability of a given UE, so that in the context of overlapped subframes the PDCCH blocking probability is lower and the system throughput is increased. The latter follows because from the UE's perspective the probability of getting a scheduled PDSCH is increased which increases the downlink data rate.